U.S. Army soldiers will soon be patrolling a 170-mile buffer zone along the southern border with Mexico in a newly created “National Defense Area” in Arizona and New Mexico.

It’s part of the Trump administration’s efforts to use the U.S. military to stop the flow of undocumented migrants into the United States.

The large swath of area will stretch 60-feet-deep along federal lands running the length of the border and will be considered a part of Fort Huachuca in Arizona, meaning that, just as at any Army base, trespassers would be apprehended by soldiers and held until turned over to law enforcement.

Some analysts see it as a way to militarize the border and skirt a federal law — the Posse Comitatus Act — that prohibits U.S. military personnel from carrying out law enforcement duties: by declaring the federal property a military base where migrants crossing into can be detained.

“Last week, President Trump signed a National Security Presidential Memorandum directing federal agencies administering federal land on the border to make land available to the Defense Department in a new national defense area,” Karoline Leavitt, the White House press secretary, told reporters on Tuesday.

“This new National Defense Area spans more than 170 miles across our border in New Mexico,” said Leavitt. “But in in the coming weeks, this administration will add more than 90 miles in the state of Texas.”

“This National Defense Area will enhance our ability to detect, interdict and prosecute the illegal aliens, criminal gangs and terrorists who were able to invade our country without consequence for the past four years under the Biden administration,” said Leavitt. “It will also bolster our defenses against fentanyl and other dangerous narcotics that have been poisoning our communities.”

U.S. officials told ABC News that the initial phase of the new area will stretch from Fort Huachuca in southeastern Arizona eastward into New Mexico.

The designation of a National Defense Area will apply only to federal lands that have been newly transferred to the control of the Defense Department and will not apply to privately held lands or territory belong to Native American reservations. That means it will be non-contiguous but will be in effect for much of New Mexico’s border with Mexico, which stretches for nearly 180 miles of the state’s border.

U.S. Army troops will be operating in what is essentially a buffer zone formally known as the Roosevelt Reservation that includes federal lands in California, Arizona, and New Mexico on the border with Mexico. In 1907, to prevent smuggling, President Theodore Roosevelt declared that a 60-foot-wide buffer zone on public lands along the border with Mexico belongs to the federal government.

Two U.S. officials told ABC News it was still to be determined whether the new authority would be applied to Texas given that the Roosevelt Reservation does not apply to lands in that state.

According to the officials, the U.S. Army will soon begin placing signs on both sides of that 60-foot buffer zone warning that they are about to enter Defense Department property and could be apprehended for trespassing.

Because of natural barriers along the border, the Roosevelt Reservation in some cases may stretch a mile into U.S. territory.

Some of the territory to now be considered an Army base already has existing fencing on the border but in some areas does not. Regardless, the Army will place signage in both English and Spanish warning that any trespassers into the area will be apprehended.

The move by the Trump administration has drawn criticism from legal analysts who describe it as a way to get around the U.S. military having law enforcement on the border which is done by U.S. Customs and Border Protection (CBP). Currently 10,000 U.S. military personnel have been authorized to serve along the border, but only in a support role to CBP.

“The president’s plan would empower U.S. soldiers patrolling the area to take on a civilian law enforcement function: apprehending and detaining migrants crossing the border into the U.S. Deploying the military to enforce civilian law is a clear violation of the Posse Comitatus Act,” said Elizabeth Goitein, the senior director of the Liberty and National Security Program at the Brennan Center for Justice.

“Under emergency powers law, the president is required to seek congressional approval for any transfer of federal land to the Defense Department,” said Goitein.